1. Field of the Invention
The present invention relates to an ink jet recording apparatus in which recording is effected by discharging ink onto a recording medium from recording means mounted to a reciprocally moving carriage.
2. Related Background Art
Recording apparatuses of serial type in which a recording operation is carried out while scanning a recording head over a recording medium have been used in various image recording applications, and, particularly, ink jet recording apparatuses have been developed greatly since image quality has been enhanced due to recent progress of high resolving power and coloring ability.
Also in the ink jet recording apparatus, although a full multi head in which discharge ports for discharging ink droplets are arranged with high density has been used, in the recording head of serial type, image formation with higher resolving power can be performed by further increasing arrangement density of the discharge ports and by reducing an ink discharging amount per one dot.
On the other hand, in order to realize image quality approaching silver salt photography, various techniques such as, for example, a technique in which six-color (cyan, magenta, yellow, black, tinted cyan and tinted magenta) recording is effected by using fundamental four color (cyan, magenta, yellow and black) inks and tinted inks having lower densities of such color inks simultaneously, have been developed. Further, countermeasure for reduction in a recording speed due to enhancement of image quality has been made by increasing element number of the recording head and/or by enhancing driving frequency and/or by using a technique such as bi-directional recording thereby to good through-put. Further, as the high image quality and high through-put have been achieved, as means for improving reliability of the recorded image, various recovery operations (wiping, preliminary discharge, suction recovery and the like) have been carried out.
The preliminary discharge is an operation (processing) for preventing occurrence of poor discharging and density difference due to drying of discharge ports (or liquid paths communicated with such discharge ports) which are not used by discharging the ink from the recording head toward a preliminary discharge receiving portion provided in a non-recording area during the recording operation. On the basis of a timing for effecting the preliminary discharge, a recording environment, a temperature of the recording head, kind of the recording medium and/or a recording mode, preliminary discharge interval, discharge position, discharge number, discharge frequency and discharge pattern are controlled. For example, there has been proposed a technique in which, regarding a recording medium such as a normal (plain) paper in which the through-put is more preferential than the image quality, the preliminary discharge (time preliminary discharge) is effected upon recording start scanning after a predetermined time period from the previous preliminary discharge is elapsed, and, on the other hand, regarding a recording medium such as a glossy paper in which the image quality is more preferential than the through-put or depending upon the recording mode, the time interval between the time preliminary discharges is shortened or the preliminary discharge (each line preliminary discharge) is effected each time upon the recording scanning. Further, in order to reduce a moving time to the preliminary discharge receiving portion, there has been proposed a technique in which the preliminary discharge receiving portion is provided within a moving range of a carriage for the recording so that the preliminary discharge is effected during acceleration or deceleration or the preliminary discharge receiving portion is provided on a platen to reduce the moving range of the carriage.
On the other hand, as a method for increasing a recordable range of the recording medium, Japanese Patent Application Laid-open Nos. 07-009714 (1995) and 2001-054955 disclose a method in which a recording medium is made recordable upon to ends of the recording medium by providing ink collecting means at a position on a platen corresponding to an end of the recording medium in a main scanning direction. Further, Japanese Patent Application Laid-open Nos. 2000-118058 and 2000-351205 disclose a method in which the recording is realized with no margins at upper and lower ends of the recording medium by providing ink absorbing means within a platen located at a position opposed to ink discharge means or by limiting discharge ports contributing to the recording (ink discharging).
However, when the recording with no margin is effected, since the recording medium during the recording or immediately after the recording cannot be held, there is a danger that the recording medium is struck against (contacted with) the carriage (including a recording head mounted thereon) due to curl of the recording medium. Such a danger is further increased when the carriage is greatly shifted from the recording medium for the preliminary discharge (for example, when the carriage is greatly shifted from a position opposed to the plane of the recording medium to a position not opposed to the plane of the recording medium. Particularly, in the ink jet serial recording apparatus in which the recording is effected by spraying the ink against the recording medium, since moisture content is apt to be changed between front and rear surfaces of the recording medium to generate curl, such a danger is apt to occur.
To avoid this, in the conventional techniques, the kind of recording media which can be recorded with no margin was limited, or a distance (sheet distance) between the recording medium and a bottom surface of a carriage (carriage unit including a carriage and a recording head) (or a lower end of the recording head) was increased so that the recording medium is not struck against (contacted with) the carriage until the curl is increased up to some extent.
However, when the kind of recoding media is limited, the advantage (characteristic) of the ink jet recording method in which various kinds of recording media can be used is lost. Further, when the sheet distance is increased, accuracy of targeting the ink droplet against the recording medium is worsened, thereby deteriorating the quality of the recording image.
Further, if the carriage (carriage unit including the recording head) is struck against the recording medium, since not only the recording medium is damaged not to be used but also the carriage cannot be moved until the struck recording medium is removed, serious error will occur, with the result that the recording operation cannot normally been continued.
On the other hand, if it is designed so that the kind of recording media is not limited and the sheet distance is varied in dependence upon the kind of the recording medium, the arrangement will become complicated and user's operation will become troublesome, which leads to increase of cost.